mariadb-columnstore-engine/utils/common/syncstream.h

/* Copyright (C) 2014 InfiniDB, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; version 2 of
   the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

/** @file */

/*
 * classes isyncstream and osyncstream provide a C++ iostream interface
 * for C stdio FILE* streams. The current implementation does not provide
 * the necessary methods to support seeking. The I/O buffering of the
 * input FILE* is used. The C++ iostream library calls syncbuf::sync()
 * for every line, so output buffering is line-by-line.
 * */

/*
#include "syncstream.h"

void copyStream(istream& iss, ostream& oss)
{
        string line;
        getline(iss, line);
        while (iss.good())
        {
                oss << line << endl;
                getline(iss, line);
        }
}

main()
{
        FILE* ifp;
        FILE* ofp;

        ...

        isyncstream iss(ifp);
        osyncstream oss(ofp);

        copyStream(iss, oss);

        ...
}
*/

#pragma once

#include <iostream>
#include <cstdio>

namespace syncstream
{
/** A streambuf implementation for C stdio FILE* streams.
 *
 * Adapted from http://www.drdobbs.com/184401305
 */
class syncbuf : public std::streambuf
{
 public:
  /** ctor */
  syncbuf(FILE* f) : std::streambuf(), fptr(f)
  {
  }

 protected:
  /** Write character in the case of overflow */
  virtual int overflow(int c = EOF)
  {
    return (c != EOF ? fputc(c, fptr) : EOF);
  }
  /** Get character in the case of overflow */
  virtual int underflow()
  {
    int c = getc(fptr);

    if (c != EOF)
      ungetc(c, fptr);

    return c;
  }
  /** Get character in the case of overflow and advance get pointer */
  virtual int uflow()
  {
    return getc(fptr);
  }
  /** put character back in the case of backup underflow */
  virtual int pbackfail(int c = EOF)
  {
    return (c != EOF ? ungetc(c, fptr) : EOF);
  }
  /** Synchronize stream buffer */
  virtual int sync()
  {
    return fflush(fptr);
  }

 private:
  FILE* fptr;
};

/** An istream adaptor for input FILE* streams */
class isyncstream : public std::istream
{
 public:
  /** ctor */
  isyncstream() : istream(&buf), buf(0)
  {
  }
  /** ctor */
  isyncstream(FILE* fptr) : istream(&buf), buf(fptr)
  {
  }
  /** const streambuf accessor */
  const syncbuf* rdbuf() const
  {
    return &buf;
  }

 private:
  syncbuf buf;
};

/** An ostream adaptor for output FILE* streams */
class osyncstream : public std::ostream
{
 public:
  /** ctor */
  osyncstream() : ostream(&buf), buf(0)
  {
  }
  /** ctor */
  osyncstream(FILE* fptr) : ostream(&buf), buf(fptr)
  {
  }
  /** const streambuf accessor */
  const syncbuf* rdbuf() const
  {
    return &buf;
  }

 private:
  syncbuf buf;
};

}  // namespace syncstream